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      <h1 class="post-title">Spring之@Primary注解</h1>

      <div class="post-meta">
        <span class="post-time"> 2020-11-05 </span>
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            <a href="/categories/java/"> java </a>
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  <h2 class="post-toc-title">文章目录</h2>
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  <ul>
    <li>
      <ul>
        <li><a href="#作用简介">作用简介</a></li>
        <li><a href="#示例代码">示例代码</a>
          <ul>
            <li><a href="#configuration类">Configuration类</a></li>
            <li><a href="#测试类">测试类</a></li>
          </ul>
        </li>
        <li><a href="#总结">总结</a></li>
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    <div class="post-content">
      <h2 id="作用简介">作用简介</h2>
<p>当Spring容器发现某个类有多个实例bean时，会优先选用带有@Primary注解的bean。</p>
<h2 id="示例代码">示例代码</h2>
<h3 id="configuration类">Configuration类</h3>
<div class="highlight"><div class="chroma">
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<td class="lntd">
<pre class="chroma"><code class="language-java" data-lang="java"><span class="kn">package</span> <span class="nn">cn.lglspace.stulab.config</span><span class="o">;</span>

<span class="kn">import</span> <span class="nn">org.springframework.context.annotation.Bean</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.springframework.context.annotation.Configuration</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.springframework.context.annotation.Primary</span><span class="o">;</span>

<span class="kn">import</span> <span class="nn">lombok.AllArgsConstructor</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">lombok.Data</span><span class="o">;</span>

<span class="nd">@Configuration</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">PrimaryAnnotationConfig</span> <span class="o">{</span>
	<span class="nd">@Data</span>
	<span class="nd">@AllArgsConstructor</span>
	<span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">Logo</span><span class="o">{</span>
		<span class="kd">private</span> <span class="n">String</span> <span class="n">name</span><span class="o">;</span>
	<span class="o">}</span>

	<span class="nd">@Bean</span>
	<span class="kd">public</span> <span class="n">Logo</span> <span class="nf">getLogo1</span><span class="o">()</span> <span class="o">{</span>
		<span class="k">return</span> <span class="k">new</span> <span class="n">Logo</span><span class="o">(</span><span class="s">&#34;1111111111&#34;</span><span class="o">);</span>
	<span class="o">}</span>
	
	<span class="nd">@Primary</span>
	<span class="nd">@Bean</span>
	<span class="kd">public</span> <span class="n">Logo</span> <span class="nf">getLogo2</span><span class="o">()</span> <span class="o">{</span>
		<span class="k">return</span> <span class="k">new</span> <span class="n">Logo</span><span class="o">(</span><span class="s">&#34;222222222&#34;</span><span class="o">);</span>
	<span class="o">}</span>
<span class="o">}</span>

</code></pre></td></tr></table>
</div>
</div><h3 id="测试类">测试类</h3>
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<td class="lntd">
<pre class="chroma"><code class="language-java" data-lang="java"><span class="kn">package</span> <span class="nn">cn.lglspace.stulab.config</span><span class="o">;</span>

<span class="kn">import</span> <span class="nn">org.assertj.core.api.Assertions</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.junit.jupiter.api.Test</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.springframework.beans.factory.annotation.Autowired</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.springframework.boot.test.context.SpringBootTest</span><span class="o">;</span>

<span class="kn">import</span> <span class="nn">cn.lglspace.stulab.config.PrimaryAnnotationConfig.Logo</span><span class="o">;</span>

<span class="nd">@SpringBootTest</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">PrimaryAnnotationConfigTest</span> <span class="o">{</span>
	
	<span class="nd">@Autowired</span>
	<span class="kd">private</span> <span class="n">Logo</span> <span class="n">logo</span><span class="o">;</span>

	<span class="nd">@Test</span>
	<span class="kt">void</span> <span class="nf">testLogo</span><span class="o">()</span> <span class="o">{</span>
		<span class="n">Assertions</span><span class="o">.</span><span class="na">assertThat</span><span class="o">(</span><span class="n">logo</span><span class="o">.</span><span class="na">getName</span><span class="o">()).</span><span class="na">isEqualTo</span><span class="o">(</span><span class="s">&#34;222222222&#34;</span><span class="o">);</span>
	<span class="o">}</span>
	
<span class="o">}</span>

</code></pre></td></tr></table>
</div>
</div><h2 id="总结">总结</h2>
<ul>
<li>示例代码中如果去掉@Primary注解，启动时会报如下错误，相同优先级相同名称的相同类实例在spring容器里只能有一个。</li>
</ul>
<blockquote>
<p><font color=red>org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name &lsquo;cn.lglspace.stulab.config.PrimaryAnnotationConfigTest&rsquo;: Unsatisfied dependency expressed through field &lsquo;logo&rsquo;; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type &lsquo;cn.lglspace.stulab.config.PrimaryAnnotationConfig$Logo&rsquo; available: expected single matching bean but found 2: getLogo1,getLogo2
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:643)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:130)</font></p>
</blockquote>
<ul>
<li>在写单元测试时不小心把cn写成了com，会报如下错误，单元测试的包必须与启动类在同一级根目录下。</li>
</ul>
<blockquote>
<font color=red>
java.lang.IllegalStateException: Unable to find a @SpringBootConfiguration, you need to use @ContextConfiguration or @SpringBootTest(classes=...) with your test
	at org.springframework.util.Assert.state(Assert.java:76)
	at org.springframework.boot.test.context.SpringBootTestContextBootstrapper.getOrFindConfigurationClasses(SpringBootTestContextBootstrapper.java:235)
	at org.springframework.boot.test.context.SpringBootTestContextBootstrapper.processMergedContextConfiguration(SpringBootTestContextBootstrapper.java:151)
</font></blockquote>

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